The invention relates to a radiating coaxial radio-frequency cable, comprising an inner conductor, a dielectric surrounding the latter and a tubular outer conductor disposed above the latter and concentric with the inner conductor, in which cable mutually separated openings are provided in the outer conductor that are disposed in a mutually offset manner in the circumferential direction of the cable and, in the longitudinal direction of the latter, are disposed along surface lines extending mutually in parallel in rows extending over the entire length of the cable (EP 0 300 147 B1).
Because of the electromagnetic energy that travels outwards through the openings, described below as xe2x80x9cslotsxe2x80x9d, in the outer conductor, radiating coaxial radio-frequency cables (referred to below as xe2x80x9cRRF cablesxe2x80x9d for short) virtually act as aerials that make possible communication between receivers and transmitters travelling relative to one another. An important field of application of RRF cables is signal transmission in tunnel sections between transmitting and receiving devices and preferably railborne vehicles. The RRF cables are intended to make possible interference-free operation even over long lengths. They are therefore intended to ensure low attenuation of the signals to be transmitted and to have, if possible, no points of reflection. In this connection, the attenuation is the sum of the cable attenuation determined by the RRF cable itself and the coupling attenuation resulting from the radiation of HF energy.
The RRF cable according to EP 0 300 147 B1 mentioned at the outset is intended for broadband operation. In the outer conductor of the latter, round holes are provided on in a first row on a surface line, whereas slots that extend in the axial direction of the cable are disposed in a second row on a surface line offset in the circumferential direction. The holes are intended for a lower frequency range, whereas the slots are intended to serve a higher frequency range. In its application, said RRF cable is limited to two frequency ranges. Measures are not provided for influencing the attenuation of the RRF cable, in particular the coupling attenuation.
The object of the invention is to develop the RRF cable described at the outset in such a way that it has as uniform coupling attenuation as possible without interfering resonance points in a large frequency range.
According to the invention, this object is achieved
in that all the slots extend essentially in the circumferential direction of the cable,
in that slots in a first row for operating a frequency range used in mobile radio are disposed in groups in a constantly repeating pattern whose first slots, viewed in each case in the axial direction of the cable, are at a mutual spacing corresponding to half the wavelength of the lowest frequency to be transmitted in the frequency range,
in that, in each group, slots are additionally provided to take account of integral multiples of the lowest frequency to be transmitted in the frequency range, and
in that further slots are situated in at least one second row on a surface line other than that of the slots of the first row and are disposed over the entire length of the cable at mutual constant spacing that is less than half the wavelength of the highest frequency to be transmitted over the cable.
Said RRF cable can be used without changes in the slot arrangement to transmit signals in a wide frequency range which also covers, in particular, the mobile radio frequencies. This is achieved, on the one hand, by the slots provided with a repeating pattern in the first row with a lowest frequency provided for mobile radio of about 800 MHz. The broadband characteristic is provided, on the other hand, by the equidistant slots, through which lower frequencies or frequency ranges can also be transmitted without interference. In their action, all the slots in the RRF cable complement one another so advantageously that the coupling attenuation can be minimized in the entire frequency spectrum to be transmitted and has a virtually constant magnitude. That is important, in particular, in the mobile-radio frequency range, in which interfering resonance points also do not occur.
The RRF cable can be produced by conventional technology, in which connection a substantial stabilization of the strip from which the outer conductor is formed can be achieved by a distribution of the equidistant slots over two rows.
Exemplary embodiments of the subject matter of the invention are shown in the drawings.
In the drawings:
FIG. 1 shows a diagrammatic view of a coaxial RRF cable known per se.
FIGS. 2 and 3 show two different embodiments of an RRF cable according to the invention having an outer conductor that is flattened at the end.
FIG. 4 shows a portion of the outer conductor with a more precise and enlarged view of an arrangement of the slots for the RRF cable according to FIG. 3.
FIG. 5 is a diagram of the variation in the coupling attenuation of the RRF cable.